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1.1 Proof

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Question 19

Leo wishes to use proof by contradiction to prove the following statement:

'The sum of a rational number and an irrational number is always irrational.'

Identify the correct starting assumption for Leo's proof.

  • The sum of every rational number and every irrational number is irrational.
  • The sum of every rational number and every irrational number is rational.
  • There exists a rational number and an irrational number whose sum is rational.
  • There exists a rational number and an irrational number whose sum is irrational.
[4]
Markscheme

1.1 Proof Questions

  1. A Level
  2. /Maths
  3. /1.1 Proof

107 exam-style questions on OCR A Level Maths 1.1 Proof, covering 1.1.1 Structure of mathematical proof, 1.1.2 Logical connectives, 1.1.3 Disproof by counter example, 1.1.4 Proof by contradiction (A-level only), and 1.1 Proof. Each one has a worked solution and a mark scheme showing where the marks go.

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